Rotax has a list of specific oils that they recommend for use in the 912 series of engines. This is because the oil also lubricates the gearbox and can put some high shear loads on the oil.
Oil temperature is an important issue with any highly tuned engines and for this reason there is an oil cooler fitted to all 912 engines in the Tanarg. There are a number of important factors with oil. At start up the oil must be thin enough to move around the engine as quickly as possible to reduce wear. The oil must attain a temperature where it burns off any condensation before the engine is shut down. When running at full temperature the oil must be thick enough to provide decent lubrication. The maximum oil temperature should not be exceeded as the additives can break down and cause problems. A synthetic oil will survive a much higher temperature than a mineral oil.
At first all Tanargs had the oil cooler mounted on the top of the engine.
As some people were having problems in hot climates with high oil temperatures, Aircreation offered a modification kit to move the oil cooler down to a position in from of the water radiator.
The ES version of the Tanarg moved the oil cooler to a position below the water radiator and outside of the fairing.
Another option (but not from the factory) is to fit an oil cooler made by a company called Laminova. This very clever item puts the oil cooler into the water coolant line. This allows faster warm up of the oil and restricts the maximum temperature of the oil to that of the coolant water.